Cerebral infarction including acute cerebral infarction and chronic cerebral infarction, also known as cerebrovascular accident or also as cerebromalacia, is caused by interruption of the blood supply to a part of the brain due to occlusion or coarctation of cerebral artery and/or vein to result in necrosis of the brain tissue or cells. The most important risk factors thereof are hypertension, heart disease, diabetes, and cigarette smoking. For remedy of the cerebral infarction, it is important to inhibit the development of necrosis due to free radical and cerebral expansion, and anticoaggulants, thrombolytic agents, such as urokinase, tissue plasminogen activator (tPA) have been used.
Arteriosclerosis, which term is often used interchangeably with atherosclerosis, is in the conditions that the walls of the arteries become thick and stiff and the blood flow to organs and tissues are restricted. Although the cause is unknown, it is suspected that it starts with damage or injury to the inner layer of an artery, and the damage may be caused by various factors, including high blood pressure, high cholesterol, an irritant (e.g. nicotine) and certain diseases such as diabetes. For the remedy of arteriosclerosis, various drugs have been used, for example, anticholesterol agents (e.g. probucol, statins, clofibrates), anti-platelet agents (e.g. aspirin), anticoagulant agents (e.g. heparin, warfarin), blood pressure controlling agents (e.g. angiotensin-converting enzyme (ACE) inhibitors, calcium channel blockers).
Renal diseases, including diabetic nephropathy, renal failure, and nephritis, are characteristic in the functional changes such as excess glomerular filtration and albuminuria and the histological changes such as glomerular sclerosis due to increase of extracellular matrix protein. It is considered that the renal diseases are caused by sustained high blood sugar, intracellular abnormal metabolism (e.g. increase of polyol pathway and hexosamine pathway, and activation of protein kinase C (PKC)) due to hyperglycemia, accumulation of advanced glycation end-products (AGE), pressure overload due to glomerular hypertension, or increased oxidant stress, and that the most important geneses of renal diseases are increased oxidant stress as well as hyperglycemia in the light of reports that active oxygen increases in the intracellular abnormal metabolism or in the process of formation of AGE (cf. Nature, 414, pp. 813-820, 2001) and that all of the increase of hexosamine pathway, the PKC activation and increase of AGEs are inhibited by inhibition of excess production of superoxide in mitochondria (cf. Nature, 404, pp. 787-790, 2000).
It is known that exacerbation of insulin resistance is important factor of diabetes onset, but the exacerbation of insulin resistance becomes not only pathogenesis of metabolic syndrome such as diabetes but also promotes the onset and development of cardiovascular diseases and renal diseases (cf. Arterioscler. Thromb. Vasc. Biol., 24, pp. 816-823, 2004), and hence, it has been considered that improvement of insulin resistance is useful for treating diabetes and diabetic complication. It is also reported that increased oxidant stress may be an important factor of inducing insulin resistance (cf. Nature, 440, pp. 944-948, 2006) and hence an oxidant stress inhibitor may be useful for the prevention and treatment of diabetes and of onset and development of renal diseases in the light of the improving activity of insulin resistance.
Although the population of diabetic patients with renal disease is increasing year by year, there has never been found a suitable therapy for treating renal diseases.
By the way, it has been known that oxygen is essential for a living body in order to maintain life, for example, to keep normal energy production and metabolism. Oxygen may be changed into so-called active oxygen in the living body. The active oxygen includes radical oxygen and non-radical oxygen. Among the active oxygen in a broad sense including lipid-related materials, the former radical oxygen includes a hydroxyl radical (.OH), an alkoxy radical, a peroxy radical, a hydroperoxy radical, a nitrogen monoxide, a nitrogen dioxide, superoxide (O2.−), etc. The latter non-radical oxygen group includes a singlet oxygen, ozone, hydrogen peroxide (H2O2), a lipid hydroperoxide, etc.
As an active oxygen which may be affective on tissue cells, there are radical oxygens of O2.− and .OH, and non-radical oxygen of H2O2 (cf. YAKUGAKU ZASSHI 122(3), pp. 203-218 (2002)). The O2.− produces oxygen and hydrogen peroxide by the action of superoxide dismutase (SOD) in the living body. Hydrogen peroxide is changed into .OH by catalytic action of iron ion, cupper ion included in cells. The hydroxyl radical attacks directly DNA, proteins in the living body. On the other hand, the hydroxyl radical reacts with lipids and thereby is converted into lipid radical and then produce lipid hydroperoxide.
Thus, these active oxygens such as .OH, H2O2, which are relative with serious diseases, are mostly caused by O2.−, and hence, it has been demanded to find a substance being capable of suppressing O2.−.